Vinylidene chloride copolymer latex coating composition

ABSTRACT

IMPROVED BARRIER COATING COMPOSITIONS OF THE VINYLIDENE CHLORIDE COPOLYMER LATEX TYPE ARE PREPARED BY CONDUCTING THE AQUEOUS POLYMERIZATION OF VINYLIDENE CHLORIDE AND OTHER COMONOMERS IN THE PRESENCE OF A SMALL AMOUNT OF EMULSIFIED PARAFFIN WAX.

A. TROFIMOW Oct. 3, 1972 VINYLIDENE CHLORIDE COPOLYMER LATEX COATING COMPOSITION Filed NOV. 8, 1971 H mjmszxm United States Patent 3,696,067 VINYLIDENE CHLORIDE COPOLYMER LATEX COATING COMPOSITION Alex Trofimow, 16 Stetson St., Brookline, Mass. 02146 Filed Nov. 8, 1971, Ser. No. 196,444 Int. Cl. C081? 45/52 U.S. Cl. 26028.5 D 5 Claims ABSTRACT OF THE DISCLOSURE Improved barrier coating compositions of the vinylidene chloride copolyrner latex type are prepared by conducting the aqueous polymerization of vinylidene chloride and other comonomers in the presence of a small amount of emulsified paraflin wax.

This invention relates to coating compositions of the vinylidene chloride copolyrner latex type. More particularly, this invention concerns an aqueous vinylidene chloride copolyrner latex composition which exhibits improved properties when coated upon conventional packaging materials.

Aqueous vinylidene chloride copolyrner latexes have been widely employed to coat packaging materials such as paper, carton board, polymeric film and metal foil. Such barrier latexes form coatings exhibiting a high resistance to moisture vapor transmission as well as good flexibility. One difficulty associated with polymeric barrier coatings such as vinylidene chloride polymer coatings is the tendency of stacks or rolled layers of stock coated with such materials to stick together or block. Another difliculty arises from the tendency of the coating to stick to and accumulate on metallic parts of machinery used to form the stock into finished packaging. To diminish blocking and to enhance the slip characteristics of the coatings, further coatings of anti-tack or slip agents have been deposited upon the barrier coating. Alternatively, the agents may be added to the latex coating composition prior to the coating operation.

It has been discovered that barrier coatings deposited from aqueous vinylidene chloride copolyrner latexes exhibit improved desirable characteristics when the polymerization of the vinylidene chloride and comonomer is carried out in the presence of an aqueous paraflin wax emulsion. The wax emulsion may be added in any manner desired prior to polymerization, but is preferably delivered to the reaction zone in admixture with the water or aqueous phase employed in the reaction. About 1 to 4 percent by weight of wax solids is employed, based upon the weight of the monomer. Surprisingly, the presence of the wax in the reaction mixture does not adversely affect the polymerization reaction. Also surprising is the discovery that the barrier coatings which have been polymerized in the presence of Wax crystallize faster than coatings made Without the wax additive or with the wax added after polymerization, that the blocking resistance of the coatings develops in a shorter period, and additionally, the solvent resistance of the barrier coatings develops at an earlier stage in the aging of the coating. Further, the flexibility of the coated board or paper remains essentially unchanged as does the moisture vapor transmission rate and the heat sealability of the coatings.

The polymerization reaction may be carried out using conventional aqueous emulsion polymerization procedures. Generally, the monomers are emulsified in water in a reaction zone in the presence of an emulsifying agent and polymerized through the agency of a Water-soluble polymerization initiator. The polymerization is usually induced by heating the aqueous emulsion to about 30 to 80 C. with agitation. After polymerization is substantially F CC complete, the pH and the total solids are often adjusted and residual monomer removed. Additional emulsifier may be added to render the latex more stable.

The monomer charge to the reaction zone comprises at least about and preferably at least about weight percent -vinylidene chloride based upon the total weight of the monomer, the remainder being at least one monoethylenically unsaturated comonomer. Illustrative of the monoethylenically unsaturated comonomers which may be used are the vinyl halides, such as vinyl chloride and vinyl bromide; the vinyl esters, such as vinyl acetate and vinyl propionate; the vinyl ethers, such as vinyl methyl ether; acrylic monomers, such as acrylic and methacrylic acid; alkyl acrylates and methacrylates such as methyl acrylate, ethyl acrylate, butyl acrylate, methyl methacrylate, 2-ethylhexyl acrylate, etc.; and acrylonitrile. Other comonomers copolymerizable with vinylidene chloride will be well known to those skilled in the art.

The emulsifying agents and polymerization initiators employed in the present process are conventional. In general, any emulsifier capable of operating in an acid medium may be employed in the polymerization process. Exemplary emulsifiers include the soluble salts of an aryl sulfate or of a long chain alkyl-aryl sulfouate such as sodium dodecyl benzene sulfonate and sodium lauryl sulfate. Any of the conventional peroxides, persulfates or am compounds can be utilized as initiators. Illustrative of suitable initiators are potassium persulfate, sodium persulfate, hydrogen peroxide, peracetic acid, benzoyl peroxide, azo-bis-isobutyronitrile, cumene hydroperoxide tertiary butyl perbenzoate; redox catalyst systems such as a combination of any of the peroxygen initiators aforementioned together with reducing agents such as sodium sulfite, sucrose, ferrous gluconate, etc. The amount of the polymerization initiator may be varied over a relatively wide range, but generally about 0.1 percent to about 0.5 percent by weight of initiator, based on the monomers, is employed.

The following examples serve to illustrate the invention more fully and are not intended to be limiting.

EXAMPLE I A l-liter, 4-neck flask equipped with stirrer and reflux condenser is charged with 350 grams of demineralized water to which has been added 1.2 grams sodium bisulfite and 22 grams of a 40% dispersion of paraflin wax in water (ALWAX 253A, a product of American Cyanamide). The flask ingredients are then heated to 40 C. A monomer mixture containing 402.5 grams vinylidene chloride, 30 grams methyl acrylate, 7.5 grams acrylonitrile, 1.1 grams acrylic acid, and 11 grams of sodium dodecylbenzene sulfonate emulsifier is prepared and transferred to a separatory funnel connected to the flask. 44 grams of the monomer mixture were added to the aqueous phase in the flask and the reaction initiated by the dropwise addition of a 2% solution of potassium persulfate. After the monomer pre-shot was reacted, the remaining portion of the monomer mixture is added continuously. The reaction is carried out under moderate reflux at 38 to 40 C. After completion of the monomer addition, the product is heated slowly to 50 C. and then allowed to cool to room temperature. The resulting latex has a total solids content of 55%. The pH of the latex was adjusted to 3.0 to 3.5 with 5% sodium pyrophosphate solution, diluted to 40% total solids and then vacuum stripped of residual monomer. The final product had a total solids content of 55%.

EXAMPLE II A latex was prepared as in Example I except that no wax emulsion was included.

3 EXAMPLE III A latex was prepared as in Example I except that the monomer mixture consisted of 92 percent vinylidene chloride and 8 percent of methylacrylate.

examined. If the spot is dull, the surface has been attacked, and solvent resistance is rated as N. If the spot is semi-shiny the coating has a partial solvent resistance, and is rated as P, P, or P+ to accord with its appearance. If the spot is barely visible, there has 5 EXAMPLEIV been no attack of solvent, and resistance is recorded as A latex was re ared as in Exam le III exce t that no or T' Wax emulsion s i p P Blockmg is measured by placing the coated stock face- All of the above latexes were coated on carton board by tofaee e Plaemg, s'pound w l a Single Pass of a #16 The rod applies the coating at the sandw1ch and allowing the weight to remain in posithe rate of about 12 per ream (3000 Square feet of t1on for 24 hours. The meaning of the figures is as follows: paper), producing a coating which is approximately 1=no bloclong occurred; 2=sl1ght blocking, but the plies mil in thickness. The coated samples were dried at a tem- Separate wlthout damage to the coating; 3=adhesion 1s perature of 122 C. for periods ranging between /2 and 5 so severe that on separation, either the coating or the minutes. The samples were subjected to tests described 15 P p Stock Was damaged; and =P y coml'llete below. The results are given in Table I. adhesion, and separation of the sheets is commerc1ally The slip angle or the angle indicative of the coefiiimpossible.

TABLE I Blocking Drying Toluene resistance MVTR at room time afternumber temperature minutes Slip ankle 16 red at 10 27 single Faee- Face- Latex 120C. fidays days days Static Kinetic pass lace back ExampleI P- P R- 14 11 .17 2 2 Example II 36 N 1 N 2 N 3 N 4 N 5 N Example III 55 R 1 R 2 3 4 5 17 1 1 Exampmw ii- 3:331:31??? -l. 1 1 2 R 3 4 5 cient of friction was measured in the following manner. EXAMPLE V A steel block weight was used which was 1.9 inches in E 1 I t th t height, 2 inches in width, and 4 inches in length, having A latex was p p l s 111 amp e excep a nfo at each end of the bottom a step 1 inch in length, 2 inches wax was p,resent durmg the Polymenzatlon reacnon' A in width, and 0.25 inch in height, which was the surface ter fermatlen of the filial pelymer e 22 grams of in contact with the latex coating being tested. The weight 0 the 40% Paraffin wax dlsperslen used m the above of the block was 4 pounds, or 1 pound per square inch amples was f q the final latex in the horizontal position. The latex coated samples to The erystalhzatfon rate measured as the percent rela' be tested were attached to a Smooth wooden hoard with tive order of coatlngs made from the latexes of Examples Scotch tape with the uncoated side of the sample adjacent H and V was tested for on a Beekman Infrared spee' to the wooden hoard. The Weight was Placed on the latex trometer IR-9, using the conventional ATR method. Tests coated Side of the Sample and the board was Slowly were made on five samples of each of the latexes, the only tilted until slippage occurred. This angle was recorded variable for each of the five samples being the time each as an indication of the static coeflicient of friction. of the five samples w allowed to 4W at In In measuring the angle indicative of h kinetic 1 the percent relative order obtained for each of the efiicient of friction, the board was raised to a predeter- 6O five test Samples of e of the E P H mined angle and the Weight was then placed on the latex andnv are Plotted g st the drying time, in minutes at coated surface of the test sample, and the weight was 120 From} 1t 1s evlden? that s of observed to see if slip occurred. The angle of the board mp whlch was Prepared accordlPg 9 the lnvsntlon, was h changed i the propeldhection and the weight exhibited the fastest rate of crystallization leading to again was l d on the coated f The angle at faster development of solvent and block resistance. which the weight slipped was reported as an indication of I clalm! the kinetic coefficient of friction. the method of Prepaflng aqueous Vinylidene Moisture vapor transmission rate (MVTR) was deterchlorlfie Polymeric latexes ussful as barrier coatings i d i accord i h TA PI standards 4 4- -45 in wherein a monomeric mixture containing at least about which the amount of water vapor transfer is reported as welght Percent Vinyhdene Chloride with P to about grams f water vapor passed b a looi h sample 20 weight percent of at least one monoethylenic comonoper 24 hour period at relative humidity and F. C(lpolymerizable therewith is emulsion polymerized The resistance of the coating to solvents is measured In the Presence of Water, emulsifier and a t u l by dropping a single drop of toluene on the coating and 75 polymerization initiator, the improvement which comallowing the toluene to evaporate. The dry spot is visually prises conducting said polymerization in the presence of from about 1 to about 4 weight percent of emulsified paraflin wax, said amount of wax being the weight percent of wax solids based upon the weight of monomers in said monomeric mixture.

2. The method of claim 1 wherein the amount of wax employed is 2%.

3. The method of claim 1 wherein said wax emulsion is introduced to said reaction zone in admixture with the water employed to form the aqueous phase.

4. The method of claim 1 wherein as least about 90 weight percent of vinylidene chloride is employed.

5. The method of claim 1 wherein said comonomer comprises at least one member from the group consisting of acrylonitrile, acrylic acid, methacrylic acid, an alkyl acrylate and an alkyl methacrylate.

References Cited UNITED STATES PATENTS 3,397,163 8/1968 Bruno 260'28.5 D 2,990,391 6/1961 Grantham 260--28.5 D 3,387,997 6/1968 Sculley 260-285 D MORRIS LIEBMAN, Primary Examiner P. R. MICHL, Assistant Examiner 

